Groaning Noise Under Acceleration

I have a 2000 Corolla LE, auto transmission, with 115,000 miles. I get a "groaning" noise from the car (engine/transaxle area?) when I start to accelerate (soft or hard) from a stop or while under way. This happens whether the car is cold or warmed up. The noise is only noticeable for a few seconds. The noise is not evident with transmission in P or N, and only, it seems, when the engine/transmission are under load (?). Any advice would be welcome. I bought the car new and all servicing is in accordance with...etc.

Most likely something in the power train or wheel components.
Could be transaxle, CV joints, drive shafts, or even wheel hub and bearings.
I have a similar sound on my Corolla and it has been like that for two years.
I believe it is CV joints, but it still drives and pulls fine when accelerating.
It kind of makes the car sound like it has power (even though it is only a 1.8L).

OK thanks for the info. I'm taking 'er in to my trusting mechanic tomorrow. I have narrowed down when it groans: between 1000-1200 RPM when the engine is loaded. I can hold the brake, put 'er in gear, and step on the gas. From idle (800 RPM) its fine until 1000 RPM. It groans and then as I pass 1200 RPM the groan stops. Same thing happens when she's rolling.

Hmm - that definitely sounds like torque converter is noisy or some resonance in the engine/transaxle to me (vibration in the engine mounts or heat shields). If you stand on the brakes and rev the engine up in that manner - having the noise present itself in a fairly narrow window with the car stationary - rules out a huge number of possibilities. Hard to tell without being right htere - but probably not driveline, suspension, or brake related.

When was the transaxles services last? Every had the pan dropped and the magnets cleaned off inside. ATF Filter changed? Hopefully Toyota Type T-IV ATF was NOT used. I have a dead transaxle downstairs in the basement because of wrong fluid type (from dealership 30K service goof - long story).

AT fluid was changed at each 30k interval. The car has not had a "pan service" or AT filter change according to my service records. Interesting that the service manual schedule doesn't list an AT pan cleaning or filter change. I'm surprised my dealer didn't try to sell me that at my 90k "Blue Sevice".

I am confused though. You said you hoped that "Toyota Type T-IV ATF was NOT used". I thought that was the only type fluid to use. Thanks for your advice thus far.